Highly fecund mothers sacrifice offspring survival to maximize fitness

Abstract

Why do highly fecund organisms apparently sacrifice offspring size for increased numbers when offspring survival generally increases with size? The theoretical tools for understanding this evolutionary trade-off between number and size of offspring have developed over the past 25 years; however, the absence of data on the relation between offspring size and fitness in highly fecund species, which would control for potentially confounding variables, has caused such models to remain largely hypothetical. Here we manipulate egg size, controlling for maternal trait interactions, and determine the causal consequences of offspring size in a wild population of Atlantic salmon. The joint effect of egg size on egg number and offspring survival resulted in stabilizing phenotypic selection for an optimal size. The optimal egg size differed only marginally from the mean value observed in the population, suggesting that it had evolved mainly in response to selection on maternal rather than offspring fitness. We conclude that maximization of maternal fitness by sacrificing offspring survival may well be a general phenomenon among highly fecund organisms.

Bet-hedging as an evolutionary game: the trade-off between egg size and number

“…This is not surprising since a very shallow slope makes the difference in survival between different propagule sizes negligible and variation in size of little value. The exact shape of the survival function in natural systems can be very hard to measure (but see Einum & Fleming 2000), but our results point at its potential importance for which type of strategy evolves.…”

Fine-scale local adaptation in an invasive freshwater fish has evolved in contemporary time

“…2 populations is necessary to show that differences are unlikely to be explained by population  habitat interactions unrelated to divergent selection (discussed by Kawecki & Ebert [1]). Non-genetic maternal effects can influence offspring performance in nature [48]; however, our results are unlikely to reflect maternal contributions as the beneficial effects of egg size erode quickly with age [32]. We attempted to minimize the influence of any lingering maternal effects by rearing individuals for several months in common-laboratory conditions prior to their release into the wild, and controlled for individual body size and condition on survival.…”

Evidence for harvest-induced maternal influences on the reproductive rates of fish populations

“…The extrapolation of results from experiments to entire populations can be problematic because parental influences might be expressed differently in the wild than in captivity (Bernardo 1996;Chambers & Leggett 1996), or might affect the relative fitness of individual adults (Einum & Fleming 2000) without affecting the reproductive rate of a population (Charlesworth 1980). While the dynamics of exploited fish stocks can behave in ways that are consistent with effects of parental influences on offspring survival (Marteinsdottir & Thorarinsson 1998;Marshall & Frank 1999;Hsieh et al 2006Hsieh et al , 2008, direct evidence of this phenomenon is limited to one study of a population of Atlantic cod (Gadus morhua) in which recruitment varied positively with the proportion of eggs spawned by older fish ( Vallin & Nissling 2000).…”